The present invention relates to semiconductor packages and fabricating methods thereof, and more particularly, to a semiconductor package which is compact in size and assured in quality, and a fabricating method thereof
A conventional QFN (Quad Flat Non-leaded) semiconductor package 10, disclosed in U.S. Pat. No. 5,172,214 as illustrated in FIG. 1, includes a semiconductor chip 11; a die pad 12 having a first surface 12a and a second surface 12b for attaching the chip 11 on the first surface 12a; a plurality of leads 13 disposed around the die pad 12 and electrically connected to the chip 11; and an encapsulant 19 for encapsulating the chip 11, the die pad 12, and the leads 13. The leads 13 each has a first portion 14 located closely to the chip 1, a second portion 16 partially exposed to the outside of the encapsulant 19, and an intermediate portion 15 for connecting the first portion 14 and the second portion 16. The second portions 16 of the leads 13 serve as I/O terminals for electronic transmission so as to electrically connecting the semiconductor package 10 by means of solder balls (not shown) to a substrate such as an external printed circuit board (not shown). Furthermore, the electrical connection between chip 11 and the leads 13 can be achieved either through gold wires 17 as illustrated in left part of FIG. 1, or through solder balls 18 by means of a TAB (Tape Automated Bonding) technique as illustrated in right part of FIG. 1. In addition, the die pad 12 has the second surface 12b thereof exposed to the outside of the encapsulant 19, allowing heat generated by the chip 11 in operation to be dissipated to the outside of the semiconductor package 10 through the exposed surface 12b of the die pad 12.
FIG. 2 illustrates another conventional QFN semiconductor package disclosed in U.S. Pat. No. 5,942,794. As shown in the drawing, this QFN semiconductor package 20 includes a semiconductor chip 21; a die pad 22 for mounting the chip 21 thereon; a plurality of leads 23 electrically connected to the chip 21 through gold wires 27; and an encapsulant 29 for encapsulating the chip 21, the die pad 22, the gold wires 27 and the leads 23. The leads 23 each has a surface 23a partially exposed to the outside of the encapsulant 29 for serving as I/O terminals for electronic transmission so as to electrically connect the semiconductor package 20 to a substrate such as an external printed circuit board (not shown). The QFN semiconductor package 20 differs from the QFN semiconductor package 10 in FIG. 1 in that the die pad 22 of the semiconductor package 20 with tie bars 25 thereof being bent upwardly is more elevated in position than the leads 23, allowing the die pad 22 to be entirely encapsulated in the encapsulant 29. Moreover, unlike the leads of the semiconductor package 10 in FIG. 1, the leads 23 in FIG. 2 are not formed with a height difference therewithin.
Unlike conventional semiconductor packages such as QFP (Quad Flat Package) and SOP (Small Outline Package), the foregoing two QFN semiconductor packages are not provided with downwardly bent outer leads, which makes the QFN packages reduced in thickness to 0.85 mm, which is about half thick as a conventional package.
However, for fabricating the foregoing OFN packages, due to lack of adequate support or clamping force during molding the encapsulant, the die pad or the leads tend to be dislocated when a molding resin is injected rapidly, allowing a small amount of the molding resin to be squeezed into spacing between the die pad or the leads and a mold. As a result, flash occurs on the exposed surface 12b of the die pad or the exposed portion of the second portions 16 of the leads of the semiconductor package 10 in FIG. 1, or flash occurs on the exposed surfaces 23a of the leads of the semiconductor package 20 in FIG. 2, so that quality of the fabricated semiconductor package is severely degraded.
The foregoing flash problem can be solved by adhering a tape to a bottom surface of the die pad and leads for preventing flash from occurrence. However, during a wire-bonding process, a cushion effect provided by the tape may cause the leads to shift in position, which definitely degrade the wire-bonding quality.
Furthermore, the 0.85 mm OFN package may be out of date according to increased demand for even thinner electronic devices, and thus it is needed to further reduce the thickness of the QFN package.
In addition, the foregoing QFN packages have the leads thereof partially exposed to the outside of the encapsulant rather than entirely encapsulated in the encapsulant, which make contact area between the leads and the encapsulant reduced, allowing bonding strength to be deteriorated as well as delamination to be generated between the leads and the encapsulant, so that quality and liability of the QFN package are detrimentally affected.
A primary objective of the present invention is to provide a semiconductor package and a fabricating method thereof, which can effectively reduce the thickness of the semiconductor package and prevent delamination from occurrence.
In accordance with the foregoing and other objectives, the semiconductor package proposed in the invention comprises: a semiconductor chip having a first surface and a second surface; a plurality of leads disposed around the chip and having the same height as the semiconductor package, with strengthening structures being formed on sides of the leads; a plurality of connecting mechanisms formed at the leads and extending from surfaces of the leads toward the chip, for being electrically connected to the first surface of the chip and the leads; and an encapsulant for encapsulating the chip, the connecting mechanisms and the leads, with at least the second surface of the chip and upper and lower surfaces of the leads being exposed to the outside of the encapsulant.
The fabricating method of the foregoing semiconductor package of the invention comprises the following steps: providing a lead frame having a plurality of leads extending from a frame of the lead frame, wherein the leads are formed with strengthening structures on sides thereof, and a plurality of connecting mechanisms extend from surfaces of inner sides of the leads; attaching a supporting carrier to a bottom surface of the lead frame; mounting a semiconductor chip having a first surface and a second surface in a space on a surface of the carrier, wherein the space is predefined by the frame of the lead frame and the leads; electrically connecting the first surface of the chip to the corresponding connecting mechanisms of the leads; performing a molding process to form an encapsulant in the space acting as a mold cavity defined by the frame of the lead frame and the leads; removing the carrier; and performing a singulating process to form individual semiconductor packages.
As concluded from the above mentioned, as compared with a conventional semiconductor package, the semiconductor package of the invention eliminates the use of a die pad, allowing the second surface of the chip to be exposed to the outside of the encapsulant, which simplifies the construction of the lead fame and makes the package further reduced to below 0.40 mm in thickness as well as improves the heat dissipating efficiency thereof.
Moreover, during the molding process, with the use of the space acting as the mold cavity predefined by the frame of the lead frame and the leads, the invention can adopt upper and lower molds with no mold cavity for forming the encapsulant, which allows the molding process to be performed for packages in various sizes, and saves the manufacturing cost for the molds. Furthermore, as the chip and the lead frame have bottom surfaces thereof attached to the supporting carrier, and the leads of the lead frame have the upper surfaces thereof tightly clamped by the upper mold, therefore a mold resin can be prevented from flashing on the exposed surfaces of the chip and the leads.
Besides, on the sides of the leads there are formed the strengthening structures, which help significantly increase bonding strength between the leads and the encapsulant for preventing delamination or crack from occurrence, so that quality and liability of the semiconductor package can be assured.
In addition, the leads have both the upper and lower surfaces thereof exposed to the outside of the encapsulant, allowing the semiconductor packages to be stacked together in a manner that the package has its upper surface abutting a corresponding lower surface of an adjacent package, so as to increase the layout density and strengthen the performance for the packages.